Journal of Plant Research

, Volume 119, Issue 3, pp 205–215 | Cite as

Diversity of secondary endosymbiont-derived actin-coding genes in cryptomonads and their evolutionary implications

  • Goro TanifujiEmail author
  • Mayumi Erata
  • Ken-ichiro Ishida
  • Naoko Onodera
  • Yoshiaki Hara
Regular Paper


In the secondary endosymbiotic organisms of cryptomonads, the symbiont actin genes have been found together with the host one. To examine whether they are commonly conserved and where they are encoded, host and symbiont actin genes from Pyrenomonas helgolandii were isolated, and their specific and homologous regions were digoxigenin (DIG) labeled separately. Using these probes, Southern hybridization was performed on 13 species of cryptomonads. They were divided into three groups: (1) both host and symbiont actin gene signals were detected, (2) only the host actin gene signal was detected, and (3) host and unknown actin signals were detected. The phylogenetic analysis of these actin gene sequences indicated that the evolutionary rates of the symbiont actin genes were accelerated more than those of the hosts. The unknown actin signals were recognized as the highly diverged symbiont actin genes. One of the diverged symbiont actin sequences from Guillardia theta is presumed to be as a pseudogene or to its precursor. Southern hybridizations based on the samples divided by pulsed-field gel electrophoresis showed that all actin genes were encoded by the host nuclei. These results possibly represent the evolutionary fate of the symbiont actin gene in cryptomonads, which was firstly transferred from the symbiont nucleus or nucleomorph, to the host nucleus and became a pseudogene and then finally disappeared there.


Cryptomonads Nucleomorph Symbiotic gene reorganization Symbiont actin gene 



We are grateful to Dr. Tatsuya Ota (The Graduate University for Advanced Studies) for his help with the pulsed-field gel electrophoresis technique. We thank Dr. Hisayoshi Nozaki (The University of Tokyo) and Dr. Hidetoshi Sakayama (National Institute for Environmental Studies) for their kind advice and suggestions. We also thank Dr. R. Jordan (Yamagata University) for critical reading of the manuscript. This work was partially supported by a Grant-in-Aid from the Ministry of Education, Science, Sports and Culture of Japan (Nos. 15255007, 1044025, and 0745423) and SOKENDAI Joint Research Program “Symbiosis and Diversity in Biosystems”.


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Copyright information

© The Botanical Society of Japan and Springer-Verlag 2006

Authors and Affiliations

  • Goro Tanifuji
    • 1
    Email author
  • Mayumi Erata
    • 2
  • Ken-ichiro Ishida
    • 3
  • Naoko Onodera
    • 1
  • Yoshiaki Hara
    • 4
  1. 1.Graduate School of Engineering and ScienceYamagata UniversityYamagata 990-8560Japan
  2. 2.Global Environmental ForumIbarakiJapan
  3. 3.Division of Life Sciences, Graduate School of Natural Science and TechnologyKanazawa UniversityKanazawaJapan
  4. 4.Department of Biology, Faculty of ScienceYamagata UniversityYamagataJapan

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